General

I currently use a Canon EF 70-200 F4 USM as a lens for astrophotography. I needed a way to mount my Mele Quieter MiniPC along side a custom power box on top of the lens, so cable management can be done in a nice way and to reduce the amount of cables that can potentially disturb the mount while tracking. Hence, I came up with this design. It will cover the focal distance gauge but I do not need it for astrophotography. I realized there might be some interest in this, so I decided to publish it and give some instructions.

Note: This is quite a specific model. Without modifications you most likely need exactly the same lens and dovetail plate for it to fit together nicely or even make it work. (See note on the dovetail in BOM section). Raw STEP and Fusion360 files are attached, so consider remixing if needed.

I highly recomment to do some quick and dirty prints of the rings in PLA just to see if the fit properly. Otherwise, see the note above.

Model specifics

• Handle can take standard finder shoe attachments (e.g. guide scope etc.)
• Lens can rotate 360 degrees inside the rings. They lock with 2 knobs quite securely.
• Hexagon outside shape that (hopefully) provides more rigidity and stability
• Could not find any more vibration compared to the original aluminium lens mount
• Fully assembled I find it quite sturdy and it fits my need.

If you print this, use at your own risk. I feel its quite durable and rigid, but its still not metal after all.

Print Materials

I used Bambu PETG-CF (mainly for the look) and Polylite PETG. Should not be a problem to swap the PETG-CF for some regular PETG.

For the support interface I have used Bambu PLA (white) and adjusted the parameters so the PETG directly prints on the PLA interface with 0 Z-distance. This resulted in a beautiful print and it was easy to remove the support.

The regular print profile uploaded does not use this, as I figured it might be too much adjustmens for people to revert. So I added a the Bambu Studio 3mf project that uses the PLA support as a separate raw file. Feel free to test it.

BOM

Heat set inserts (Thread x Length x Diameter):

• 5pcs M3 x 4 x 5 (used for the Handle to be able to use M3 scres as locking screws for attachments)
• 4pcs M4 x 6 x 6 (used on the top side of both rings to attach the handle)
• 6pcs M5 x 6 x 7 (used for the tensioning knobs and the bottom of the rings to attach the bottom plate)
• 2pcs M6 x 8 x 8 (used on the bottom plate to attach the whole rig to the aluminium dovetail plate)

Note: I got this box for heat set inserts: https://amzn.eu/d/jiEppDI

Screws (Thread x Length):

All screws are cylinder head hex screews from a local hardware store.

• 2pcs M3 x 10 (used to secure finder shoe attachements to the handle)
• 2pcs M4 x 16 (used to attach the handle to the top of the rear ring)
• 2pcs M4 x 12 (used to attach the handle to the top of the front ring. SEE NOTE BELOW)
• 4pcs M5 x 10 (used to attach the bottom plate to the bottom of the rings)
• 2pcs M5 x 16 (used to create the tensioning knobs)
• 2pcs M6 x 16 (used to mount the full rig to the dovetail plate)

Note: I did not buy M4 x 12 screws. I used a dremel to cut them to length. After that I put them in a drill and used a file at an angle to remove any burrs. The screw cannot exceed 12mm length otherwise it will not fit and damage the ring. You might be getting away with M4 x 10mm screws but I did not test that as I had them cut already for a previous prototype.

Screws I used: https://amzn.eu/d/4N5jWOH

Hex nuts:

• 4pcs M4 locking nuts

I got them in bulk from the hardware store. Any locking M4 hex nut should do.

Felt Tape:

This is used on the inside of the rings for a few reasons.

• Provide the right level of friction, so the lens can turn when not secured by the knobs
• Reduces the inner diameter slightly so the knobs can clamp down with enough force and optimize clearance
• Helps to protect the finish of the lens

The tape I used: https://amzn.eu/d/eA6vcIT

Dovetail plate:

I bought this specific one: https://www.teleskop-express.de/de/montierungen-stative-schellen-schienen-stromversorgung-14/prismenklemmen-schienen-montierungsadapter-82/prismenschienen-308/ts-optics-stabile-gp-level-prismenschiene-l-228-mm-mit-langloechern-7940

Note: The bottom plate of the rig has a guiding knob that slides into the center cut of the dovetail from above. If you have a different dovetail you might need to remove the knob. It can be done in Bambu Studio by adding a negative part and fitting it in. Height of the bottom plate: 10mm, height of the knob: 5mm (from the top of the bottom plate)

Build and assembly

• Print ;-)
• Apply all heat set inserts and melt them in (let it cool before assembly)
• Cut the felt tape to length and apply it on the inside of the rings. For the rear piece, I use the full width of the ring. For the front piece, I prefer to only have tape on the parts that actually grip on the lens.
• Screw the longer M5 screw through the bottom piece of the knob. Apply glue to the inside of the bottom piece before screwing it all the way in. Apply glue to the top piece of the knob to glue it in place. I also applied glue to the piece that fits the hex hole.
• Push in the M4 hex nuts. It can be tight, the model does not have a lot of clearance there. I used an M5 bolt to push them in properly
• Use the longer M4 screws to attach the handle to the rear ring top piece
• Use the shorter M4 screws to attach the handle to the front ring top piece
• Use the M5 screws to attach the bottom plate to both bottom ring pieces
• Put the lens in the bottom part of the rig, put the top part on and screw the parts together with the remaining long M4 screws.
• Screw the knobs in and tighten to preference.

Note: The lens won't rotate as easily as with the original metal rig that comes with it. Thats fine for me, as prefer to not accidentily rotate too much. Feel free to adjust to your liking in the raw files and remix it. I would not advise to skip the felt tape for this purpose.